Method for using probe card

ABSTRACT

An apparatus for use with a wafer prober and a probe card comprising a stiffening member having a feature defining a first plane. The stiffening member is mountable atop the central portion of the probe card. A reference member is provided to mount to the wafer prober and has an underside with a feature defining a second plane. When the feature of the stiffening member defining the first plane is urged against the feature of the reference member defining a second plane the probe tips of the probe card are substantially planarized relative to the wafer prober.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. utility patentapplication Ser. No. 10/902,188 filed Jul. 28, 2004 now U.S. Pat. No.7,098,650, and claims the benefit of U.S. provisional patent applicationSer. No. 60/490,621 filed Jul. 28, 2003, the entire content of which isincorporated herein by this reference.

FIELD OF THE INVENTION

The present invention relates generally to systems for testingintegrated circuits in wafer form and, more particularly, to apparatusfor planarizing probe cards for use therewith.

BACKGROUND OF THE INVENTION

Manufacturers in the electronics industry use automatic test systems ortesters to test various electronic components, integrated circuits (ICs)and other devices under test (DUTs) to cull out defective devices. Forexample, data patterns are delivered to an integrated circuit withspecific timing and voltage settings through timing generators and pinelectronic channels to test the functionality of the integrated circuit.Data is then read from the integrated circuit to ensure that the deviceresponds correctly. A variety of parametric timing tests may also beperformed to validate correct operation of the integrated circuit aswell as adherence to its specifications. Generally, it is desirable totest integrated circuits at several points during the manufacturingprocess, including while they are still part of a wafer or substrate.

Equipment used in wafer testing can include a wafer prober and anautomated test system. A conventional wafer prober has a movable chuckwhich serves to transport the wafer to a position underlying a probecard mounted to the top deck of the wafer prober by being clamped at itsperiphery. A probe array is typically provided on the underside of theprobe card for engaging the bonding pads of one or more die on thewafer. A plurality of contact elements, electrically coupled with theprobe array, are usually provided at the periphery on the top of theprobe card. The automated test system includes one or more testers whichoverlie the top deck of the wafer probe and have an electrical interfacefor electrically engaging the contact elements of the probe card.

Unfortunately, changes in temperature and mechanical forces experiencedby the probe card during testing can result in distortion of the probecard, thus deflecting the generally unsupported central portion of theprobe card where the probe array is located. The larger the probe card,the more deflection can occur in the probe card. Such distortion of theprobe card can result in undesirable alignment errors between the probearray of the probe card and the chuck, thus compromising the accuracy orcompleteness of the testing of die carried by the chuck.

In view of the foregoing, it would be desirable to minimize distortionof the probe card, particularly in the vicinity of the probe arraymounted to the underside of the probe card.

SUMMARY

An apparatus for use with a wafer prober and a probe card comprising astiffening member having a feature defining a first plane is provided.The stiffening member is mountable atop the central portion of the probecard. A reference member is provided to mount to the wafer prober andhas an underside with a feature defining a second plane. When thefeature of the stiffening member defining the first plane is urgedagainst the feature of the reference member defining a second plane theprobe tips of the probe card are substantially planarized relative tothe wafer prober.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of an automatic test system and waferprober using the apparatus for planarizing a probe card of the presentinvention.

FIG. 2 is an exploded, schematic side elevational view of a portion ofthe automatic test system and wafer prober of FIG. 1 showing theapparatus for planarizing a probe card of the present invention.

FIG. 3 is a schematic, perspective view of the wafer prober of FIG. 1having a top deck with a reference plate thereon.

FIG. 4 is a schematic, top plan view of a probe card for use with theapparatus for planarizing a probe card of FIG. 2.

FIG. 5 is a schematic, side elevational view taken along the line 5-5 ofFIG. 4, of the probe card of FIG. 4.

FIG. 6 is a perspective view of a latching plate of the apparatus forplanarizing a probe card of FIG. 2.

FIG. 6A is an enlarged view of a portion of the latching plate of FIG. 6indicated by the circle 6A of FIG. 6.

FIG. 7 is a top plan view of the latching plate of FIG. 6.

FIG. 7A is an enlarged view of a portion of the latching plate of FIG. 6indicated by the circle 7A of FIG. 7.

FIG. 8 is a top plan view of the apparatus for planarizing a probe cardof FIG. 2 in a first position.

FIG. 9 is a cross-sectional view of the apparatus for planarizing aprobe card of FIG. 2 taken along the line 9-9 of FIG. 8.

FIG. 10 is a top plan view the apparatus for planarizing a probe card ofFIG. 2 positioned relative to the reference plate of the wafer prober.

FIG. 11 is a top plan view, similar to FIG. 8, of the apparatus forplanarizing a probe card of FIG. 2 in a second position.

FIG. 12 is a cross-sectional view, similar to FIG. 9, of the apparatusfor planarizing a probe card of FIG. 2 taken along the line 12-12 ofFIG. 11.

FIG. 13 is a top plan view, similar to FIG. 8, of the apparatus forplanarizing a probe card of FIG. 2 in a third position.

FIG. 14 is a cross-sectional view, similar to FIG. 9, of the apparatusfor planarizing a probe card of FIG. 2 taken along the line 14-14 ofFIG. 13.

FIG. 15 is a top plan view, similar to FIG. 8, of the apparatus forplanarizing a probe card of FIG. 2 in a fourth position.

FIG. 16 is a cross-sectional view, similar to FIG. 9, of the apparatusfor planarizing a probe card of FIG. 2 taken along the line 16-16 ofFIG. 15.

FIG. 17 is a schematic, side elevational view of the apparatus forplanarizing a probe card of FIG. 2 in an engaged position.

FIG. 18 is a schematic side elevational view, similar to FIG. 2, of aportion of the automatic test system and wafer prober of FIG. 1 showingthe apparatus for planarizing a probe card of FIG. 2 in an engagedposition.

FIG. 19 is a schematic top plan view of a wafer prober utilizing anotherembodiment of the apparatus for planarizing a probe card of the presentinvention.

FIG. 20 is a schematic, cross-sectional view of the wafer prober of FIG.19 taken along the line 20-20 of FIG. 19.

FIG. 21 is a schematic, top plan view of a circular probe card for usewith the apparatus for planarizing a probe card of FIG. 19.

DETAILED DESCRIPTION

FIG. 1 illustrates the main components of a wafer testing system 14,namely a wafer prober 15 and an automated test system 20. Although anysuitable wafer prober can be utilized, a suitable wafer prober is of thetype manufactured as model number UF3000 by Accretech located in Tokyo,Japan. Wafer prober 15 generally includes a wafer loader 17, controls 19and a housing 21 provided with a top deck 22 and an access door 24 (seeFIG. 1).

Automated test system 20 can be of any suitable type, such as of thetype disclosed in copending U.S. application Ser. No. 10/170,916 filedJun. 12, 2002, the entire content of which is incorporated herein bythis reference. The automated test system 20 includes one or moretesters and as shown a single tester 25 having a test head 26. Thetester 25 is supported above the wafer prober 15 by a support arm 27that is vertically adjustable on a post 28 upstanding from a wheelablebase 29. The system 20 further includes controls 30. FIG. 2 shows aschematic and enlarged view of portions of the wafer prober 15 and testsystem 20 and specifically the interface between the test head 26 andthe wafer prober 15 for performing automated wafer testing. The waferprober 15 includes a movable chuck 30, located behind the access door 24of the wafer prober, having a top substantially planar surface 32 onwhich a wafer 33 is placed. Typically, top deck 22 of the wafer prober15 is a reference plane to which probe manufacturers planarize chuck 30so that the top deck 22 is therefore planar and parallel with respect tothe top surface 32 of the chuck 30. A plurality of die (not shown) havebeen formed on the wafer 33, each have a plurality of bonding pads,contact pads or other contact interconnects formed on its top surface.

Each test head 26 includes an electrical interface 36, for exampleinput/output blocks, for outputting test signals to the die undergoingtesting and receiving response signals from the die to be analyzed bythe automate test system 20 (see FIG. 2). The electrical interface 36includes a plurality of test pins 38 for electrically connecting thetest head 26 to the probe card 34 and hence to the die electricallyconnected to the probe card 34. The test pins 38 are arranged to contacta corresponding plurality of contact pads 39 on the probe card 34, whichare illustrated in FIG. 4.

The system of the invention further includes a reference member or plate42 mounted to or integral with the top deck plate 22 of the prober 15(see FIGS. 2 and 3). The reference plate 42, more clearly illustrated inFIG. 3 which shows a perspective top view of the wafer prober 15 withoutthe test head 26, is supported above the probe card 34 by the top deck22. Reference plate 42 preferably bridges over the central opening intop deck 22, as shown in FIG. 3, and is more preferably centered overthe top deck. The reference or support member 42, which can be a thick,highly planar plate made from any suitable material such as metal orceramic. Reference member 42 preferably has a feature defining a plane,which is preferably on the underside of the reference member 42. Suchfeature is planar with the top deck 22, and hence parallel to and planarwith respect to the top surface 32 of the chuck 30, and is preferably aplanar bottom surface 44. To achieve a high degree of planarity forreference surface 44, the reference plate 42 is preferably made from arigid material, for example a metal such as steel or aluminum. Accessopenings 46 are provided between the reference plate 42 and the top deck22 to permit the electrical interface 36 of the test head 26 to accessthe underlying probe card 34.

A probe card 34 is carried by the wafer prober and provides anelectrical interface between the one or more test heads 26 of the testsystem 20 and a die of the wafer 33 undergoing testing (see FIG. 2).Probe card 34 includes a substrate layer which can be made from anysuitable dielectric material and is preferably a printed circuit board(PCB) 48 having a first or top surface 49 and an opposite second orbottom surface 50 (see FIGS. 4 and 5). A plurality of contact pads 39are formed on the top surface 49 of the PCB 48 and are preferablylocated in a peripheral portion 52 of the probe card 34. The contactpads 39, some of which are shown in FIG. 4, are arranged in one or morepatterns and accessible from the top of the probe card 34. The pluralityof test pins 38 of the test head 26 are arranged in a corresponding oneor more patterns as the pattern of contact pads 39 to permit contact andregistration of the test pins 38 with the contact pads 39. Contact pads39, including pluralities of distinct arrays thereof, can extendpartially or completely around the peripheral portion 52 of the probecard 34. Accordingly, it is appreciated that the invention is broadenough to cover cards 34 having contact pads 39 disposed only atportions of the periphery 52, such as along two sides as shown in FIG.4. The probe card 34 can further include a substrate member, for exampleblock 54 made from ceramic or any other suitable material, secured orrigidly coupled to the bottom surface 50 of the PCB 48 and locatedwithin a central portion 56 of the probe card 34. The central portion 56of the card 34 is preferably that portion of the card 34 interior ofcontact pads 39 and more preferably that portion of the card 34 beneaththe central portion of the reference plate 42.

A probe array or assembly 58 descends or depends from thecentrally-disposed block 54, which supports the probe array 58 (see FIG.5). The probe elements or probes 59 of the probe array 58 are arrangedin a pattern corresponding to the pattern of contact bonding pads orballs of the die undergoing testing. Each of the probes 59 has a probeend or tip which registers with and engages a contact pad of the diewhen the probe array 58 engages the wafer 33. The probe tips of theprobe array 58 are aligned in a plane, sometimes referred to herein asthe plane of the probe array 58. Electrical leads are provided in theprobe card 34, for example conductive traces (not shown) within the PCB48, for electrically coupling the contact pads 39 on the top surface 49of the PCB 48 to the probes 59 of the probe array 58 descending from thecentral portion 56 of the underside of PCB 48.

The probe card 34 preferably further includes a stiffening member orplate 60 attached to the top surface 49 of the PCB 48 within the centralportion 56 of the probe card 34 (see FIGS. 4 and 5). The stiffener plate60 is preferably made from any suitable rigid material such as metal andmay be attached to the PCB 48 by screws (not shown). The stiffener plate60 adds rigidity to the central portion 56 of the probe card 34. Theprobe card 34 further includes three or more planarizing adjustmentscrews 62 for adjusting the plane of the probe array 58, andspecifically the plane formed by the tips of the probes 59, with respectto the plane of the stiffener plate 60. More specifically, screws 62permit the plane of the probe array 58 to be made substantially parallelto the plane of the stiffener plate 60.

The central portion of probe card 34, and preferably stiffener plate 60,includes a feature defining a plane. Such feature is preferably aplurality of at least three alignment elements 65 are attached to thestiffener plate 60 within the central portion 56 of the probe card 34and extend outwardly, and preferably upwardly, from the probe card 34(see FIGS. 4 and 5). The alignment elements 65 have top surfaces 68 andare arranged on the stiffener plate 60 such that the top surfaces 68substantially define a plane. As shown in FIG. 4, the alignment elements65 are spaced apart so as to form the shape of a triangle, preferably anequilateral triangle, when viewed in plan. The alignment elements 65 arepreferably made out of metal that can be machined with a high degree ofaccuracy. The plane formed by the top surfaces 68 of the alignmentelements, that is the feature of the probe card defining a plane, ispreferably substantially parallel to the plane of the plane of the probearray 58 and preferably the plane of the stiffener plate 60.

A means or cooperating mechanism is included for urging the feature ofthe probe card 34 defining a plane against the reference member 42 andpreferably the feature of the reference member 42 defining a plane. Inthe illustrated embodiment, such means or apparatus 69 includesalignment elements 65 and serves to make the plane formed by the tips ofprobes 59 planar or parallel with the bottom surface 44 of referenceplate 42. Apparatus 69 can part of a cooperating mechanism of theinvention that is carried by the reference member 42 and the centralportion of the probe card 34 for rigidly coupling the central portion ofthe probe card 34 to the reference member 42. Such cooperating mechanismand apparatus 69 preferably include a latching mechanism 70 mounted tothe reference plate 42 for latching the alignment elements 65 of theprobe card 34 to the reference plate 42. Preferably, the latchingmechanism 70 lifts and urges the top surface 68 of the alignmentelements 65 against the bottom, planar surface 44 of the reference plate42. Latching mechanism 70 is rigidly coupled to wafer prober 15, andpreferably to top deck 22 thereof. In one preferred embodiment,illustrated herein, the latching mechanism is bolted or otherwiserigidly secured to reference plate 42.

Gripping or latching mechanism 70 according to one embodiment of theinvention includes a latch member or plate 171 having a first or topsurface 172 and an opposite second or bottom surface 173 (see FIGS. 6and 7). A plurality of holes or slots 176 adapted to engage or receiveat least a portion of respective alignment elements 65 extend throughsurfaces 172 and 173 of the latching plate. The alignment elements orlatch pins 65 are preferably in the form of mushroom latch pins withindentations such as annular groves 177 extending around the cylindricalbody of the alignment element for facilitating latching of the element65 by the plate 171 (see FIGS. 2 and 9). Each keyhole slot 176 includesan enlarged opening 178 large enough for the head 179 of an alignmentelement 65 to pass therethrough and an inner ledge 180 that slides intothe groove 177 of the alignment element 65 to engage the alignmentelement 65 beneath the head 179 of the element 65.

The gripping or latching assembly or mechanism 170 further includes alift plate 182 positioned above the latch plate 171, as shown in FIGS. 8and 9. Side portions 184 of the latch plate 171 extend beyond the liftplate 171, as shown in FIG. 8, and underneath the reference plate 42 ofthe wafer prober 15, shown in phantom lines in FIG. 8 and solid line inFIG. 9. The keyhole slots 76 are located within the side portions 184 ofthe latch plate 171 and are therefore not covered by the overlying liftplate 182. The lift plate 182 is mechanically coupled to the underlyinglatch plate 171 by six mechanical couplers or fasteners 185. Thelatching mechanism 70 includes an actuator or mechanism 186, shownschematically in FIG. 8, that is mechanically coupled to the lift plate182 for moving the lift plate 182 and the latch plate 171 mechanicallycoupled to the lift plate 182 laterally and upwardly. The actuator maybe of any suitable type, such as pneumatic, hydraulic, electric,mechanical or any combination of the foregoing.

Each mechanical coupler 185, one of which is illustrated in some detailin FIG. 9, is preferably from an I-shaped body or pin 187 extendingthrough the lift plate 182. The pin 187 has a flanged top end 189 seatedagainst a spring 191 and a flanged bottom end 194 seated in a key shapedslot 195, similar to slot 176, formed in the latch plate 171. The spring191 is preferably a suitable stack of bellevelle washers extendingconcentrically around the pin 187 and seated or disposed within a cavityor bore 196 formed in the lift plate 182. The spring 191 biases the pin187 by having a first or top end rest or push against the top end 189 ofthe pin 187 and the second or bottom end rest or push against an innersurface of a flange 196 forming the bottom of cavity 192.

FIG. 10 shows a top view of the latching mechanism 70 relative to thereference plate 42 of the wafer prober 15. The lift plate 182 ispositioned within an opening 194 of the reference plate 142. The sideportions 184 of the latch plate 171 are positioned beneath the referenceplate 42, and therefore not visible in FIG. 10, so as to position thekeyhole slots 176 located within the side portions 184 beneath the lowerplanar surface 44 of the reference plate 42. FIG. 9 shows one of thekeyhole slots 176 beneath the lower planar surface 44 of the referenceplate 42.

In the method of operating and using apparatus 69, latching mechanism 70engages and lifts the alignment elements 65 upwardly to urge the topsurfaces 68 of the alignment elements 65 against the bottom planarsurface 44 of the reference plate 42. A latching sequence utilizingapparatus 69 is described with reference to FIGS. 8-17. The operatorinitially loads probe card 34 into wafer prober 15 by means of accessdoor 24. The probe card 34 is placed onto an internal mechanism of thewafer prober (not shown) which delivers the probe card to a positionbeneath latching mechanism 70, which position is similar to the positionillustrated in FIG. 9 where only a portion of the probe card 34 isshown. Such internal mechanism aligns elements 65 with the largeopenings 178 of the keyholes slots 176, as illustrated in FIGS. 8 and 9,and then raises the alignment elements 65 to align grooves 177 of theelements 65 with the inner ledges 180 of the keyhole slots 176, asillustrated in FIGS. 11 and 12. The lift plate 171 is then slidlaterally by the actuator 186 referred to above, thereby sliding thelatch plate 171 coupled to the lift plate 182 laterally. This causes theinner ledges 80 of the keyhole slots 176 to engage the annular grooves177 of the alignment elements 65 (see FIGS. 13 and 14). The lift plate182 is then raised upwardly by the actuator, thereby lifting the latchplate 147 upwardly until all of the top surfaces 68 on the heads 179 ofthe alignment elements 65 engage the bottom planar surface 44 of thereference plate 42 (see FIGS. 15 and 16). The probe card 34 iselectrically connected to the die by having the chuck 30 mechanicallyposition the wafer 33 so that bonding pads of the die contact respectiveprobe elements or probes 59 of the probe card 34.

The nonrigid attachment of the latch plate 171 to the lift plate 182, bymeans of couplers 185, permits the latch plate to separate from the liftplate as necessary to accommodate any misalignment between the plates171 and 182, such as the top surface of the latch plate 171 not beingparallel to the bottom surface 44 of the reference plate 42 when all ofthe top surfaces 68 of the alignment elements 65 have engaged thereference plate 42. More specifically, each of the couplers 185 canfloat within its respective cavity 192 to permit such movement betweenplates 171 and 182. Springs 191 serve to urge or push against theflanged top ends 189 of couplers 185 so as to continually urge topsurfaces 168 of the alignment elements 65 against the planar surface 44of the reference plate 42 regardless of any such movement of latch plate171 relative to lift plate 182. The amount of each such spring force canbe predetermined by adjustment of the amount that the spring 191 isinitially compressed within the lift plate 182. Preferably, thealignment elements 65 are urged against the planar surface 44 withsufficient force to prevent translation and rotation of the alignmentelements 65, and the probe card 34 attached thereto, relative to thereference plate 22 during the operation of system 14.

FIG. 17 shows the probe card 34 attached to the reference plate 22 andthus wafer prober 15 by means of apparatus 69 and latching mechanism 70thereof. As shown therein, as well as in FIG. 16, a gap 196 existsbetween the bottom surface of latch plate 171 and the top surface ofstiffener plate 60 when the probe card 34 has been referenced andaffixed to the reference plate as described above. Gap 196 desirablyaccommodates any irregularities, misalignments or lack of planaritybetween the stiffener plate 60 and the reference plate 22 which mayexist prior to the operation of system 14 or which may come about as aresult of changes in temperature or mechanical forces experienced by theprobe card 34, during the operation of the system 14.

As can be seen, apparatus 69 and the method of the present inventionserve to planarize the top surfaces 68 of the alignment elements 65 withthe bottom planar surface 44 of the reference plate 42 and hence the topsurface 32 of the chuck 30. Because the plane of the probe array 58 isplanar with the plane of the top surfaces 68 of the alignment elements65 and the plane of such top surfaces 68 is planar with the plane of thechuck 30 when urged against the planar surface 44 of the reference plate42, the plane of the probe array 58 is planar with the plane of thechuck 30 so as to facilitate proper engagement of the probe array 58with die on the wafer 33 and thus accurate testing of such die. In thelatched state, the latching mechanism 70 thus firmly holds the centralportion 56 of the probe card 58 planar with the chuck 30.

The system of the invention offers advantages over the prior art. Oneadvantage is that distortions of the probe card 34 outside the centralportion 56 of the probe card 34 have minimal effect on planarization ofthe probe array 58 because the central portion 56 is held planar by thereference plate 42. FIG. 18 illustrates how distortions of the PCB 48 ofthe probe card 34 do not affect the planarization of the probe array 58.Apparatus 69 can thus reduce the need to provide a stiffener plateextending beyond the central portion 56 of the probe card 34 to maintainplanarity of the probe array 58, thereby reducing the weight of theprobe card 34.

Another advantage is that the reference plate 42 adds rigidity to thecentral portion 56 of the probe card 34 by holding the central portion56 planar to the reference plate 42. In addition, the reference plate 42does not increase the thermal mass of the probe card 34 because thereference plate 42 is thermally isolated from the probe card 34 by a gap96, assuming negligible thermal conduction through the alignmentelements 65. As a result, the reference plate 42 is subject tosignificantly less thermal distortion during temperature testing of thewafer. Low thermal mass is important because it reduces the timerequired for the temperature of the probe card 34 to stabilize duringtemperature testing of the wafer.

Apparatus 69, and the method of the present invention, serve to rigidlycouple or secure the central portion 56 of the probe card 34 to thebridging support member 42 and thus to wafer prober 15. In the preferredembodiment, the peripheral portion 52 of the probe card 34 is free ofthe reference plate 42, that is not supported by the reference plate 42or the wafer prober 15. Notwithstanding the foregoing, the invention isbroad enough to cover methods and apparatus where some small portion orpercentage of the peripheral portion 52 of the probe card 34 iscontacted by the wafer prober, for example for purposes other thansupporting the probe card 34. The invention is also broad enough tocover methods and apparatus where some small portion or percentage ofthe peripheral portion 52 of the prober card 34 is supported by thewafer prober, such as by the reference plate 42 or top probe deck 22, solong as the main or significant proportion or majority of the weight ofthe probe card 34 is supported by the central portion 56 of the card 34.

Supporting probe card 34 substantially or preferably solely by thecentral portion 56 advantageously serves to free the peripheral portion52 of the probe card 34 for other purposes. For example, freeing theperipheral portion 52 of the probe card from support pins or othersupport elements can expand the methods and means by which test head 36can engage the probe card 34.

The invention can be used to planarize the probe arrays of various typesof probe cards, including circular and other nonrectangular-shaped probecards. In another embodiment of the apparatus for planarizing a probecard of the present invention, a reference plate 242 for use with acircular probe card 234 is provided. The reference plate 242, shown on acircular top deck 222 of a wafer prober 215 in FIGS. 19 and 20, has acentral portion 245 with spokes 247 extending therefrom and attaching toor integral with the circular top deck 222. The spokes 247 rigidlysupport the reference plate 242 above the circular probe card 234, aperipheral portion 252 of which is shown in FIG. 19 underlying thereference plates 242. Contact pads 239 are provided on the upper surfaceof the substrate layer or printed circuit board 248 of the card 234. Forsimplicity, only a single array of the contact pads 239 are shown inFIG. 19. Spokes 247 are arranged to provide access openings 249therebetween so that an appropriately configured test head 36 can accessthe underlying probe card 234, and specifically contact pads 239thereon. The latching mechanism and reference planar surface (notshown), similar to latching mechanism 70 and reference planar surface 44described above, are located in the central portion 245 of the referenceplate 142.

The circular probe card 234, shown in plan in FIG. 21, includes astiffener plate 260 within a central portion 256 of the probe card 234and exemplary arrays 240 of contact pads 239 arranged in a ring along aperiphery 252 of the probe card 234. A probe array, not shown butsimilar to probe array 58 described above, descends from a bottom of theprobe card 234 within the central portion 256. Three or more alignmentelements 265, which can be substantially similar to alignment elements65 described above, are attached to the stiffener plate 270 withincentral portion 156 and extend upwardly from the probe card 234. Thealignment elements 256 cooperate with reference plate 234 in the mannerdescribed above to planarize or make parallel the probe array withrespect to the top surface of the chuck (not shown) of the wafer prober215. More specifically, the top surfaces of the alignment elements 265are urged against the bottom planar surface of the reference plate 242.

It should be appreciated from the foregoing that the reference member orplate of the present invention can be configured and shaped toaccommodate any sized and shaped probe card. As discussed above, forexample, the reference plate can be rectangular or circular in plan.Openings or apertures can be provided in the reference plate, in anysuitable configuration, for permitting access to the contact pads of aprobe card positioned beneath the reference plate. For example, roundreference plate 242 is provided with spokes which define openingstherebetween for accessing arrays of contact pads 239 provided on acircular probe card 234.

It is appreciated that the feature of the reference member defining aplane referenced above is not limited to a planar surface but can be ofany suitable configuration. For example, such feature can be a pluralityof spaced-apart, outwardly-extending alignment elements like elements 65above. Similarly, the feature of the probe card defining a plane is notlimited to the spaced-apart outwardly-extending alignment elements 65discussed above, but can be of any suitable configuration. Thus, forexample, outwardly-extending alignment elements, such as alignmentelements 65 above, can be provided on reference member or plate 42 orelsewhere on the wafer prober, instead of on stiffening plate 60 asdiscussed above. Where, for example, the alignment elements depend fromthe reference plate 42 and have end surfaces defining a plane that isparallel to the upper surface 32 of the chuck 30, a planar referencesurface is provided on the probe card, for example as the upper surfaceof stiffening plate 60, which is parallel to the plane of the probearray 58. A latching assembly or mechanism, for example similar tolatching mechanism 70, can be mounted on the top of the central portionof the probe card for gripping the alignment elements of the referencemember in the manner described above with respect to mechanism 70.Alternatively, when the alignment elements are provided on the referencemember or elsewhere on the wafer prober the latching assembly ormechanism can be rigidly coupled to the wafer prober, such as toreference member 42 as described above, for gripping a set of couplingelements extending upwardly from the stiffening plate 60 or elsewhere onthe central portion of the probe card. Such an embodiment could thushave alignment elements depending from the reference member and couplingelements, for example similar to alignment elements 65, upstanding fromthe stiffening plate 60. It is further appreciated that any referenceplane of the invention can be formed from a single surface or a set ofdistinct surfaces that extend in a single plane.

Although a latching mechanism was employed in the preferred embodiment,other means may be employed to urge the top surfaces of the alignmentelements of the apparatus of the present invention against the bottomplanar surface of the reference plate. For example, the entire probecard may be raised toward the reference plate so that the top surfacesof the alignment element abut against the bottom planar surface of thereference plate. This may be done, for example, by securing the probecard to a movable plate capable of raising and lowering the probe card.The probe card may be grasped, clamped or otherwise moved at itsperipheral portion or any other portion.

As can be seen from the foregoing, an apparatus for planarizing a probecard has been provided which minimizes distortion of the probe card,particularly in the vicinity of the probe array mounted to the undersideof the probe card. The apparatus can include a plurality, preferably aplurality of at least three, alignment elements disposed in the centralportion of the probe card for aligning the planarity of the probe arrayprovided on the underside of the probe card with a reference plate of awafer prober. The alignment elements can be urged against a referenceplane of the reference plate by being grasped by a latching mechanism orby engaging any other portion of the probe card so as to urge thealignments elements secured thereto against the reference plate.

We claim:
 1. A method for using a probe card having a central portionprovided with a stiffening member for adding rigidity to the centralportion and a plurality of alignment elements and having a peripheralportion with a wafer prober having a reference member and a test headcomprising urging the alignment elements against the reference member,securing the central portion of the probe card to the wafer prober, theperipheral portion of the probe card extending free of the wafer prober,and engaging the probe card with the test head.
 2. The method of claim 1wherein the central portion has a depending probe assembly and a featuredefining a plane and wherein the wafer prober is provided with a topdeck having the reference member, further comprising urging the featurein the central portion of the probe card defining a plane against thereference member to align the probe assembly relative to the waferprober.
 3. The method of claim 2 wherein the plurality of alignmentelements provide the feature defining a plane and include at least threespaced-apart, upwardly-extending alignment elements having respectiveend surfaces substantially defining the plane.
 4. The method of claim 3wherein the reference member has a bottom surface extendingsubstantially in a plane and wherein the urging step includes urging thefeature of the probe card defining a plane against the bottom surface ofthe reference member.
 5. The method of claim 2 wherein the feature ofthe probe card defining a plane is a planar surface.
 6. The method ofclaim 1 wherein the wafer prober has a top probe deck provided with thereference member and wherein the securing step includes securing thecentral portion of the probe card to the reference member.
 7. The methodof claim 1 wherein the test head has test pins and wherein the probecard has contact elements on the peripheral portion, and wherein theengaging step includes electrically coupling the test pins of the testhead with the contact elements of the probe card.
 8. The method of claim1 wherein the engaging step includes engaging the peripheral portion ofthe probe card with the test head.
 9. A method for using a probe cardhaving a central portion provided with a stiffening member for addingrigidity to the central portion and a plurality of alignment elementsand having a peripheral portion provided with contact elements with atest head having electrical elements and with a wafer prober having areference member, comprising urging the alignments elements against thereference member, securing the central portion of the probe card to thewafer prober so that the peripheral portion of the probe card extendsfree of the wafer prober and engaging the contact elements of the probecard with the electrical elements of the test head.
 10. The method ofclaim 9 wherein the central portion has a depending probe assembly and afeature defining a plane and wherein the wafer prober is provided with atop deck having the reference member, further comprising urging thefeature in the central portion of the probe card defining a planeagainst the reference member to align the probe assembly relative to thewafer prober.
 11. The method of claim 9 wherein the wafer prober has atop probe deck provided with the reference member and wherein thesecuring step includes securing the central portion of the probe card tothe reference member.
 12. A method for using a probe card having acentral portion provided with a stiffening member for adding rigidity tothe central portion and a plurality of alignment elements and having aperipheral portion and opposite first and second surfaces with a waferprober having a reference member and a test head comprising urging thealignment elements against the reference member, securing the centralportion of the probe card to the wafer prober so that the peripheralportion of the probe card extends free of the wafer prober and engagingthe first surface of the peripheral portion of the probe card with thetest head.
 13. The method of claim 12 wherein the wafer prober has a topprobe deck provided with the reference member and wherein the securingstep includes securing the central portion of the probe card to thereference member.
 14. The method of claim 12 wherein the test head hastest pins and wherein the probe card has contact elements on theperipheral portion, and wherein the engaging step includes electricallycoupling the test pins of the test head with the contact elements of theprobe card.